Detecting and Preventing Type flaws: a Control Flow Analysis with Tags 1

A type flaw attack on a security protocol is an attack where an honest principal is cheated on interpreting a field in a message as the one with a type other than the intended one. In this paper, we shall present an extension of the LySa calculus with tags attached to each field, indicating the intended types. We developed a control flow analysis for analysing the extended LySa, which over-approximates all the possible behaviour of a protocol and hence is able to capture any type confusion that may happen during the protocol execution. The control flow analysis has been applied to a number of security protocols, either subject to type flaw attacks or not. The results show that it is able to capture type flaw attacks on those security protocols.